Every household and many businesses require hot water for everyday use. These hot water consumers typically rely on conventional storage water heaters to store and constantly heat water for production upon demand.
A variety of fuel options are available for conventional storage water heaters, including electricity, natural gas, oil, and propane. Ranging in size from 20 to 80 gallons (75.7 to 302.8 liters), storage water heaters remain the most popular type for residential heating needs in the United States. A storage heater operates by releasing hot water from the top of the tank when the hot water tap is turned on. To replace that hot water, cold water enters the bottom of the tank, ensuring that the tank is always full.
Because the water is constantly heated in the tank, energy can be wasted even when no faucet is on. This is called standby heat loss. It is possible to completely eliminate standby heat losses from the tank and reduce energy consumption 20% to 30% with demand (tankless) water heaters, which do not have storage tanks. Cold water travels through a pipe into the unit, and either a gas burner or an electric element heats the water only when needed.
Tankless water heaters save energy because they do not need to constantly heat water in a large storage tank. To achieve this, tankless water heaters instantaneously heat water as it is passing from the consumer's water supply to the outlet (e.g. faucet or showerhead). The tankless water heater, therefore, needs to “know” when hot water is in demand in order to function properly. Flow switches are used to signal the tankless water heater that the consumer desires hot water. Briefly, when a consumer turns on a faucet or a dishwasher, any hot-water-requiring device, water flows from the water supply through the tankless water heater system. This flow of water causes the flow switch to activate the heating element (e.g. gas or electric) of the tankless water heater.
U.S. Pat. No. 5,408,578 to Bolivar (the '578 patent), the contents of which are incorporated herein by reference, describes a continuous flow water heater assembly requiring no storage tank and including an entrance chamber having a flow control switch mounted therein adapted to be activated upon a positive flow of water through the system. The water flows from the entrance chamber to a plurality of heating elements each of which are at least partially segregated by virtue of their being removably mounted within separate heating chambers. The heating chambers are attached in fluid communication to one another by a plurality of at least two ports which are of proportionately different sizes such that water will be passed between the first and second heating chambers in proportionately different amounts through the different sized ports. According to the '578 patent, water is thereby distributed between the heating elements so as to prevent exposure of the heating elements when activated and thereby eliminate either of the heating elements from being exposed to air and thereby subject to burnout.
U.S. Pat. No. 5,479,558 to White, Jr. et al. (the '558 patent), the contents of which are incorporated herein by reference, describes a compact tankless water heater that is characterized as delivering heat in proportion to demand. A flow responsive valve energizes an electrical control system and is purely flow responsive, even to minute flow, and consumes no power when dormant. An electronic control system is connected to power by the flow switch, and is substantially de-energized when dormant. Most electronic components of the control system are mounted on the flat front wall of the pressure vessel. Thus, the '558 patent is characterized as having minimized overall dimensions with cool water serving as a heat sink and heat generated by electronic controls being captured for heating purposes. In particular, triacs control the heating elements and are cooled to prolonging their life.
Further, the inventor is unaware of tankless electric hot water heaters that supply power to the heating elements to heat the water in a proportion that varies based on the amount of water that must be heated and the temperature difference between the temperature of the water and the temperature to which the water must be heated. Instead, most tankless electric hot water heaters merely supply 100% of the maximum power or 0% of the maximum power, i.e., completely on or completely off. This is not as efficient a method of heating water as one would prefer.